Blinding Us With Science

Rust. It’s as much a part of our hobby as dinosaur squeezin’s. No matter where it is, it has to go, and there are a number of ways to get it gone. Sand or bead blasting is the most popular. It is fast and efficient, and home blast cabinets are within reach of most of us. A wire wheel on a bench grinder, and a wire cup on an angle grinder, are also pretty efficient, but their applications are limited and won’t get rust out of pits.

Naval jelly is a time-honored method, and we’ve used common household vinegar many times with good results. Vinegar is a mild acid that eats rust, but like any acid it also eats the base metal, as does naval jelly.

Two other methods are gaining in popularity. The first is submerging parts in a tank filled with a mixture of molasses (the kind mixed with cattle feed) and water for a few hours and then rinsing off the rust. Rust removal happens everywhere the liquid touches the piece, and it doesn’t dissolve the base metal. While this method is very cheap, nicely biodegradable, and decidedly nontoxic, the mixture smells like an open sewer.

The other method is a bit more mad scientist: electrolysis. Rust is a chemical reaction in which iron combines with moisture in the air to form iron oxide. Electrolysis uses a low-voltage electrical current to break the chemical bond between rust and the base metal, leaving the base metal untouched while the rust falls off or is easily wiped away. As with molasses, rust is removed evenly from everywhere the liquid touches (even from deep pits), the base metal doesn’t diminish, and it’s low-effort. We like to use this method for machined surfaces that we don’t want to abrade by bead blasting or wire wheeling.

Here’s how you do it. Suspend your rusty part in a container and pass an electrical current from the part through the solution to an anode, another piece of steel suspended in the solution across from the part. As the current passes from the part through the solution to the other piece of metal, the bond between rust and steel is broken. After anywhere from an hour to 12-plus hours, the part is completely rust-free. You can’t overdo the process.

The solution is water mixed with washing soda, available at any grocery store. The soda solution is a very mild base (the opposite of acid), but you should use gloves and keep it away from your eyes. The process also releases hydrogen and oxygen from the water in small amounts over time. Since oxygen is flammable and hydrogen is explosive, work in a well-ventilated area (outside), don’t cover the container while cleaning parts or else the gas will collect, and keep open flame and sparks away.

The most obvious source of sparks is the power source, typically a battery charger. Yes, we’re leery of hooking battery charger leads to metal submerged in water. The voltage is fairly low (12 or 6 volts), and there aren’t enough amps to hurt you. But make sure the charger is unplugged before playing with the clamps, and keep your hands out of the solution while it’s working.

The other piece of metal the current flows to is sacrificial and will eventually wear away. Some use stainless steel as the anode, but stainless contains chromium, which the electrolysis releases, creating hexavalent chromium in your solution. Dump that in your yard and Erin Brockovich will be knocking on your door. Stick with basic steel as the anode, and the solution will be totally biodegradable and environmentally friendly. The process also doesn’t remove oxidation from nonferrous metal, like aluminum, and can, in fact, erode the aluminum part you’re trying to clean.

We set up a simple electrolysis tank with a plastic bucket, some steel flat stock, and a rod. Some people keep the solution stored in the shop for future use, but it’s so cheap you should make a fresh batch when needed. We’ve heard concerns about the process causing hydrogen imbrittlement, which can weaken the piece. We’re not saying it can’t happen, but considering the low amount of voltage and low temperatures used, we don’t see it as a problem compared to chroming suspension components like street rodders do.

Electrolysis is an efficient method, pioneered by archeologists to strip heavy rust off artifacts that were buried for centuries. It’ll make short work of the rust on your car parts.